1. Field of the Invention
The present invention relates to a positioning structure, and more particularly to a positioning structure for cutting machines or grinder machines.
2. Description of Related Art
With reference to FIG. 5, a conventional positioning structure 70 is mounted on a head 80 of a cutting machine or a grinder machine. The head 80 of the cutting machine or grinder machine is a cylinder and has a rear face, a driving apparatus, and a mounting hole 81. The driving apparatus is mounted in the head 80. The mounting hole 80 is formed in the rear face of the head 80. The conventional positioning structure 70 is connected to the head 80 and has a rotating shaft 71 and a positioning ring 72. The rotating shaft 71 is mounted in the mounting hole 81 of the head 80 and is connected to the driving apparatus, so the rotating shaft 71 may rotate relative to the head 80. The rotating shaft 71 has a distal end and a fixing portion 711, and the distal end of the rotating shaft 71 is distal from the mounting hole 81. The fixing portion 711 is formed on and protrudes axially from the distal end of the rotating shaft 71. A diameter of the fixing portion 711 is smaller than a diameter of the rotating shaft 71, thus forming a connecting portion formed on a rear face of the rotating shaft 71. The connecting portion of the rotating shaft 71 is a stepped face. An outer surface of the fixing portion 711 is a threaded face, and an inner surface of the positioning ring 72 is a threaded face. The threaded face of positioning ring 72 is screwed with the threaded face of the fixing portion 711 of the rotating shaft 71.
When the cutting machine or the grinder machine is operated, a user may loosen the positioning ring 72 from the fixing portion 711 first, and then mount a cutting disk 90 or a grinder disk around the fixing portion 711 of the rotating shaft 71. The cutting disk 90 or the grinder disk is circular and has a center and an assembling hole 91, and the assembling hole 91 is formed through the center of the cutting disk 90 or the grinder disk. The assembling hole 91 of the cutting disk 90 or the grinder disk is disposed around the fixing portion 711 of the rotating shaft 71, and the cutting disk 90 or the grinder disk abuts the stepped face between the rotating shaft 71 and the fixing portion 711. The positioning ring 72 is screwed with the fixing portion 711 of the rotating shaft 71 and is pressed against the cutting disk 90 or the grinder disk. The positioning ring 72 is screwed with the fixing portion 711 of the rotating shaft 71, the cutting disk 90 or the grinder disk abuts the stepped face between the fixing portion 711, and the rotating shaft 71, and the positioning ring 72 is pressed against the cutting disk 90 or the grinder disk. Therefore, the cutting disk 90 or the grinder disk rotates with the rotating shaft 71 synchronously. The cutting machine can cut things by the cutting disk 90, and the grinder machine can grind things by the grinder disk.
However, the fixing portion 711 of the rotating shaft 71 of the conventional positioning structure 70 corresponds in size to the assembling hole 91 of the cutting disk 90 or the grinder disk. When a size of the assembling hole 91 of the cutting disk 90 or the grinder disk changes, the rotating shaft 71 of the positioning structure 70 needs to be changed to a new size corresponding to the size of the assembling hole 91 of the cutting disk 90 or the grinder disk, and this makes the conventional positioning structure 70 of the cutting machine or the grinder machine inconvenient in use. So the conventional positioning structure 70 of the cutting machine or the grinder machine should be improved.
To overcome the shortcomings of the conventional positioning structure for cutting machines or grinder machines, the present invention provides a positioning structure for cutting machines or grinder machines to mitigate or obviate the aforementioned problems.